Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.57	9.320%	$91.3587	$91.36	$91.35	$91.40
Purchase #2	$16.65	11.822%	$18.6184	$18.62	$18.60	$18.60
Purchase #3	$134.39	12.692%	$151.4468	$151.45	$151.45	$151.40
Purchase #4	$76.64	4.193%	$79.8535	$79.85	$79.85	$79.90
Purchase #5	$185.51	3.232%	$191.5057	$191.51	$191.50	$191.50
Purchase #6	$246.52	6.525%	$262.6054	$262.61	$262.60	$262.60
Purchase #7	$96.31	5.313%	$101.427	$101.43	$101.45	$101.40
7 purchase totals =	$839.59		$896.8155	$896.83	$896.80	$896.80